1. Field of the Invention
The present invention relates to a charging apparatus and a charging system for a portable electronic device.
2. Description of the Related Art
A portable electronic device such as a cellular phone obtains its operating power from a secondary battery and it is necessary to charge the secondary battery periodically.
In current cellular phones, contact charging is mainly performed in which an AC adapter is directly connected to the connector of a cellular phone or the exposed electrode of the phone is brought into contact with a terminal portion provided on a charging stand. In the contact charging, there appears to be a phenomenon of a charging failure due to contamination of a metal portion as an electrical contact or poor contact of a connector portion.
On the other hand, contactless charging, that is, charging without an electrical contact is performed using a mechanism in which power is transferred from a primary side to a secondary side by the magnetic induction of coils. In general, by only putting a device such as a phone as the secondary side on a charging stand as the primary side, it is possible to configure a charging circuit without a metal contact. Such contactless charging is employed in a cordless phone, a watch, an electric toothbrush, and the like.
The problem of the contactless charging is that when a metallic foreign object (e.g., coin) in place of a correct device is put on the charging stand, eddy currents induced by electromagnetic induction may cause the heating of the foreign object. In order to avoid this problem, there is proposed a method, such as described in Japanese Patent Application Laid-Open No. 2002-34169, for changing a charging load in a predetermined pattern by turning on/off a charging control transistor for charging a secondary battery and detecting whether or not the object put on the charging stand is a correct device by detecting at the charging stand side this change.